name: External PR Scope Guard

# Advisory check that surfaces what a NON-MEMBER pull request may change.
# Members (write/admin) and the repo's own automation bot (bump SHA PRs) are unrestricted and
# skip this check. For a non-member PR this fails unless the PR is an in-scope external
# contribution per .github/scripts/external-pr-scope.js: it changes ONLY
# .claude-plugin/marketplace.json, the delta is additions-only (no existing entry modified or
# removed), and every ADDED entry's source.url is a repo that ALREADY backs a live plugin in
# this marketplace (the allowed set is derived from the live marketplace — there is no
# maintained allowlist).
#
# Do NOT add this job to branch protection as a required status check. The merge gate is the
# `validate` + `scan` checks plus a maintainer approval; this guard is advisory signal for the
# reviewer, not a hard gate. (Making it required would block the no-approval bump-merge path.)
#
# Security: runs on pull_request_target but checks out only the BASE repo (trusted) for the
# shared script; the head marketplace.json is fetched as DATA via the API and parsed, never executed.

on:
  pull_request_target:
    types: [opened, synchronize, reopened]

permissions:
  contents: read
  pull-requests: read

jobs:
  scope-guard:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4   # base repo (trusted)
      - uses: actions/github-script@v7
        with:
          script: |
            const { evaluate, isExemptAuthor } = require(`${process.env.GITHUB_WORKSPACE}/.github/scripts/external-pr-scope.js`);

            // Members (write/admin) and the repo's own automation bot (bump SHA PRs) are
            // unrestricted; only genuinely external contributions are scope-checked.
            const ex = await isExemptAuthor({ github, context });
            if (ex.exempt) {
              console.log(`${ex.reason} — scope guard not applicable.`);
              return;
            }

            const result = await evaluate({ github, context });

            if (!result.ok) {
              core.setFailed(
                `Scope guard: a non-member PR may only ADD marketplace.json entries whose source repo already backs a live plugin here.\n - ` +
                result.problems.join('\n - ')
              );
              return;
            }
            console.log(`Scope guard passed: adds ${result.added.join(', ') || 'none'}, all from repos already live here.`);